1. Field of the Invention
The present invention relates to an apparatus for generating a time duration signal, in particular for controlling fuel metering or ignition processes in internal combustion engines. The apparatus utilizes a computer.
2. Prior Art
In both open-loop and closed-loop control or regulation of internal combustion engines, computers are increasingly being used to enable the furnishing of precise control signals for the individual final control elements and valves, especially with a view to attaining minimal fuel consumption and the least-toxic exhaust gas possible. A computer system is known from German laid open application 28 50 534 now U.S. Pat. No. 4,250,858, in which, among other variables, the injection time of fuel injection valves is ascertained in a computer in the form of a numerical value, and this value is then converted into a time related signal. This number-to-time conversion is accomplished over a predetermined number of counting-out processes of a predetermined value in a counter. Since this counter counts down continuously beginning with the same initial value A, the total duration of the output signal with the circuitry disclosed herein follows the formula: EQU ti=A.multidot.(1/fcl).multidot.k
where A is the respective initial value of the counter, fcl is the counting frequency and k indicates the total number of counting processes. The total time is thus composed of the sum of various identical individual time ranges A/fcl. In the known apparatus, this initial value A is first computed, and then the total number k of required counting processes.
It has now been found that despite the relative simplicity of this number-to-time converter, the expenditure for hardware is not insubstantial, since in consideration of the respective predetermined initial value of the counter, an intermediate memory for this initial value is required. On the other hand, given the high-quantity production of computer-controlled systems for motor vehicles, the expenditure for hardware should preferably be as low as possible, while a possibly somewhat greater expenditure for software might be more likely to be acceptable.